Positively operated steam generator



July 1,1969 K. EVERS POSITIVELY OPERATED STEAM GENERATOR Sheet Filed D60. 22, 1967 Inventor KONRAD Evens July 1, 1969 K. EVERS 3,452,722

POSIT IVELY OPERATED STEAM GENERATOR I Filed Dec. 22. 1967 Sheet 2 of a Fly. 2

Inventor.- KQNRAD E VERS 4 04 T' OZEYS July I, 1969 K. EVERS 3,452,722

POSITIVELY OPERATED STEAM GENERATOR I Filed Dec. 22,.19e7 Sheet 9 of a Inventor.- KQNRAD VERS n gmvsys United States Patent US. Cl. 122448 4 Claims ABSTRACT OF THE DISCLOSURE The temperature measuring device is disposed in the pipeline between the heat exchange point and the evaporator to measure the temperature of the operating medium flowing to the evaporator. The temperature measuring device emits a signal which causes a signal convertor to adjust the control valve in the discharge line of the separator or in the fuel supply line so as to vary the transfer of heat in the heat transfer point. As the measured temperature increases the heat transfer is reduced in the heat transfer point. This accomplishes a substantial stable heat transfer behavior in the steam generator.

This invention relates to a positively operated steam generator. More particularly, this invention relates to a positively operated steam generator having controls for controlling the heat transferred to the operating medium flowing to the evaporator.

Steam generators having an evaporator and a superheater have been known to have a liquid separator connected between the evaporator and superheater. These liquid separators have been connected by a liquid discharge pipe to the operating medium pipe leading to the evaporator so that the heat contained in the discharged liquid is transferred to the operating medium flowing to the evaporator. Generally, in these steam generators, the supply of feed water to the steam generators has been adjusted as a function of the quantity of vapor emerging from the separator and as a function of the level of liquid in the separator. The supply of fuel on the other hand has generally been adjusted as a function of the live steam pressure. However, from the point of view of control technique, the transference behavior of a circuit comprising the evaporator, separator and a heat exchanger has a tendency to fluctuate. This means that, for example, when disturbance occurs on the fire side, i.e. where a change in the heat incidence on the evaporator is caused by a change in the quantity or in the heat value of the fuel, the quantity of steam emerging from the separator fluctuates considerably. Thus, the constancy of the temperature of the live steam emerging from the steam generator is undesirably affected.

Accordingly, it is an object of the invention to damp the fluctuations occurring on the fire side of a positively operated steam generator.

It is another object of the invention to damp the fluctuations occurring on the fire side of a positively operated steam generator in a circuit consisting of evaporator, liquid separator and heat exchange point.

Briefly, the invention provides a steam generator having a circuit comprised of an evaporator, liquid separator, and heat exchange point with an apparatus to measure the temperature of the operating medium flowing to the evaporator at a location between the evaporator and heat exchange point. In addition, a signal convertor is connected to the measuring apparatus to emit a derivative action signal as a function of the measured temperature to an adjusting element which influences the exchange of heat from the discharged liquid from the separator to the operating medium flowing to the evaporator.

In operation, in the case of a sudden change in the temperature of the operating medium flowing to the evaporators, a derivative action signal to counteract this change is transmitted to the adjusting element controlling the heat transfer. This signal serves to damp the temporary change in heat transfer from the discharged liquid to the operating medium flowing to the evaporator at the heat exchange point and, hence, the change in the quantity of steam emerging from the separator is counteracted.

In one embodiment, the adjusting element for controlling the heat transfer is constructed as a valve and is disposed in the line carrying the liquid from the separator. The signal convertor in this embodiment activates the valve in a manner such that with a rise in temperature of the operating medium flowing to the evaporator, the discharge of liquid from the separator is temporarily reduced.

In another embodiment, the adjusting element for controlling the heat transfer is constructed as a valve and is disposed in the fuel supply line of the steam generator. The signal convertor in this embodiment activates the valve in a manner such that with a rise in temperature of the operating medium flowing to the evaporator, the supply of fuel is increased. This allows a greater proportion of steam to be produced in the evaporator so that less liquid is available in the separator for heat transfer with the operating medium flowing to the evaporator.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 diagrammatically illustrates a positively operated steam generator according to the invention;

FIG. 2 diagrammatically illustrates a modified positively operated steam generator according to the invention having a superimposed recycling of the operating medium; and

FIG. 3 graphically illustrates the comparitive operation of the steam generator of the invention.

Referring to FIG. 1, the steam generator 5 includes an economiser 6, an evaporator 7, and a superheater 9 within a combustion chamber. A feed water reservoir 1 is connected by a pipeline 14 to the economiser 6 and feed water is fed from the reservoir 1 to the economiser 6 by a feed pump 2 in the line 14. In addition, a flow control valve 3 is disposed in the pipeline 14 to control the flow of feed water as well as a pair of steam heated preheaters 4. The economiser 6 is connected via a pipeline 18 which passes through a heat exchange point in a heat exchanger 16 to the evaporator 7. The evaporator 7 connects with a liquid separator 8 downstream of the superheater 9 so that liquid can be separated from the steam passing on to the superheater 9. The liquid separator 8 has a discharge pipe 17 which leads through the heat exchanger 16 to the feed water reservoir 1. A valve 15 is disposed in the discharge pipe 17 to control the flow of liquid through the pipe 17 and, thus, through the heat exchanger 16. The superheater 9 connects with a turbine 10 which drives a generator 19 while the turbine outlet leads to a condenser 11 and thence through a condensate pump 12 and a pair of steam-fired preheaters 13 to the feed water reservoir 1.

A temperature measuring device 25 is provided in the pipeline 18 between the heat exchanger 16 and evaporator 7 to measure the temperature of the operating medium flowing to the evaporator 7. The temperature measuring device 25 is connected via a signal line 26 to a signal convertor 27 which is operatively connected to the valve 15 in the discharge pipe 17 for actuating the valve 15 in response to the signals received from the signal line 26.

Also, a steam volume measuring device 20 is provided in the line between the separator 8 and superheater 9 to measure the volume of steam passing from the separator 8 to the superheater 9. The steam volume measuring device 20 is connected to a controller 22 which is operatively connected to the flow control valve 3 in the feed water pipeline 14 via a signal line 28 for actuating the valve 3 in response to the signals received from the measuring device 20. The actuation of the flow control valve 3 is also controlled as a function of the level of liquid in the separator 8. To this end, a liquid level measuring device 21 is interposed in the liquid separator 8 to sense the liquid level and to emit a signal in response to the detected level through a controller 23 to the signal line 28 for controlling the actuation of the flow control valve 3.

In order to fire the steam generator 5, a burner assembly 29 is positioned in the combustion chamber. The burner assembly 29 is supplied with fuel through a pipe 30- in which a control valve 32 is positioned for controlling the amount of fuel delivered to the burner assembly 29. The valve 32 is actuated as a function of the pressure of the steam leaving the steam generator. For this purpose, a pressure measuring device 31 is positioned in the line between the superheater 9 and turbine to sense the steam pressure in the line. The pressure measuring device 3-1 emits a signal in response to the measured pressure via a controller 35 and a signal line 36 to the fuel control valve 32 for controlling the actuation of the valve 32.

During normal operation of the steam generator, feed water is drawn from the reservoir 1 by means of the feed water pump 2 and fed through the pipeline 14 to the economiser 6 and thence through the pipeline 18 to the evaporator 7. The burning fuel in the burner assembly 29 then heats the feed water in the evaporator 7. The steam/ water mixture emerging from the evaporator 7 is then separated into water and steam in the separator 18. The steam then flows into the superheater 9 and from there into the turbine 10. The steam expanded in the turbine 10 is precipitated in the condenser 11 and the condensate is fed back into the reservoir 1 by means of the condensate pump. The water separated in the separator 8 is carried away through the discharge pipe 17 to the reservoir 1 so that the heat contained in the discharged liquid is transferred in the heat exchanger 16 to the operating medium flowing to the evaporator 7.

During this time, the quantity of feed water supplied to the economiser 6 is controlled as a function of the quantity of steam passing from the separator 8 as measured by the steam volume measuring device 20 and as a function of the liquid level in the separator 8 as measured by the liquid level measuring device 21. The quantity of feed water is maintained at a rate so that the liquid level in the separator 8 fluctuates as little as possible. In other words, the liquid level is maintained as constant as possible.

In the event of a sudden rise in the temperature of the operating medium flowing to the evaporator 7, for example, due to a relatively small incidence of heat of the evaporator 7 caused by a reduced fuel supply, the signal convertor 27 receives a sudden input signal from the temperature measuring device 25 via the signal line 26. This input signal generates a derivative action signal in the signal convertor 27 which acts on the valve in the liquid discharge pipe 17 to actuate the valve 15 so as to temporarily reduce the quantity of liquid discharged from the separator 8. Thus, as less liquid flows through the heat exchanger 16, the heat transfer from the discharged liquid to the operating medium flowing to the evaporator is reduced. This reduction in heat transfer counteracts the sudden rise in temperature of the operating medium.

The steam generator can be modified from the above described steam generator in that the liquid discharged from the separator can be recycled. For example, re-

ferring to FIG. 2 wherein like reference characters are used to indicate like parts as in FIG. 1, the liquid discharge pipe 17 is void of any flow control valve or heat exchanger and communicates directly with the pipeline 18 through a recycling device 34 at a heat transfer point 33 upstream of the evaporator 7. Thus, upon a transfer of heat from the discharged liquid to the operating medium flowing to the evaporator 7, a mixture of the two flows occurs.

In addition, the signal convertor 27 instead of being used to control the flow of discharge liquid is operatively connected via the signal line 36 to the fuel control valve 32 in the fuel supply pipe 30 in order to actuate the valve 32 in response to the temperature of the operating medium flowing to the evaporator 7. In this manner the signal from the temperature measuring device 25 is superimposed on any signal from the steam pressure measuring device 31 to regulate the flow of fuel to the burner assembly 29.

In operation, upon a sudden rise in the temperature of the operating medium flowing to the evaporator 7, a sudden input signal originates in the signal line 26 to cause actuation of the valve to allow a corresponding temporary increase in the fuel supplied via the pipe 30 to the burner assembly 29. By reason of this temporary increase in the supply of fuel, more water is evaporated in the evaporator 7 so that the quantity of liquid separated off in the separator 8 and recycled through the pipe 17 is reduced. Thus, at the heat transfer point 33, less heat is given off to the operating medium flowing to the evaporator 7.

Referring to FIG. 3, the heat transfer behavior of the steam generator of the invention is significantly enhanced over that of the heretofore steam generators of the same type. For example, as shown, a sudden increase in load, AF/F, causes a change in the flow of steam AD/D emerging from the separator. In the case of a steam generator which is void of a temperature measuring device 25 and signal converter 27, the change in steam flow follows the curve a. However, in the case of the steam generators of the invention, the change in steam flow follows the curve b. It can be seen from a comparison of these two curves, that in the case of the behavior corresponding to curve a, fluctuations are brought into the circuit consisting of evaporator, separator and heat exchanger whereas in the case of the behavior corresponding to curve b, a stable heat transfer behavior is accomplished.

It is noted that the temperature of a superheatedly operated tube at the end of the evaporator 7 of the steam generator of FIG. 1 can be measured so as to produce a corresponding temperature signal which can be used to control the actuation of the flow control valve 3 in the feed water pipeline. Such a signal can be superimposed with any signal emitted by the steam volume measuring device 20 in response to the quantity of steam emerging from the separator to control the quantity of feed water supplied to the steam generator. The signal which is emitted by the level measuring device 21 to indicate the liquid level in the separator then acts on the flow control valve 15 in the liquid discharge pipe 17 along with the derivative action signal of the signal convertor 27 to control the flow of discharge liquid to the heat exchange point.

It is also noted that instead of influencing the supply of fuel according to the steam pressure flowing to the turbine 10, the supply of fuel can be influenced by the speed of the turbine 10 or by the frequency of the generator 19.

What is claimed is:

1. In combination with a positively operated steam generator having an evaporator, a pipeline upstream of said evaporator for feeding operating medium into said evaporator, a heat exchange point in said pipeline, a liquid separator downstream of said evaporator for separating steam and water therein, a superheater downstream of said separator for receiving steam therefrom, and a discharge pipe connecting said separator to said heat transfer point for conveying discharged water from said separator to said heat exchange point for heat transfer with the operating medium fed to said evaporator; a temperature measuring device in said pipeline between said heat exchange point and said evaporator for measuring the temperature of the operating medium fed to said evaporator, and means responsive to said temperature measuring device for controlling the transfer of heat from the discharged water in said discharge pipe to the operating medium fed to said evaporator at said heat exchange point.

2. The combination as set forth in claim 1 wherein said means includes a flow control valve in said dis charge pipe for controlling the flow of discharged water to said heat exchange point, and a signal convertor operatively connected between said temperature measuring device and said valve to receive a signal from said temperature measuring device in response to the measured temperature in said pipeline and to emit a derivative action signal in response to said received signal to said valve for actuating said valve to vary the flow of discharged water therethrough whereby upon a rise in measured temperature in said pipeline, the flow of discharged water is reduced.

3. The combination as set forth in claim 2 Which further comprises a heat exchanger at said heat exchange point, said operating medium pipeline passing through said heat exchanger and said discharge pipe being connected to said heat exchanger to convey the discharged water over said pipeline in said heat exchanger in a heat transfer relation.

4. The combination as set forth in claim 1 which further comprises a burner assembly for heating said evaporator and said superheater, and a fuel supply pipe connected to said burner assembly for supplying a flow of fuel thereto, and wherein said means includes a flow control valve in said fuel supply pipe for controlling the fiow of fuel to said burner assembly and a signal convertor operatively connected between said temperature measuring device and said valve to receive a signal from said temperature measuring device in response to the measured temperature in said pipeline and to emit a derivative action signal in response to said received signal to said valve for actuating said valve to vary the flow of fuel therethrough whereby upon a rise in measured temperature in said pipeline, the flow of fuel is increased.

References Cited FOREIGN PATENTS 7/1939 Great Britain. 5/1966 Canada. 

